I am currently running my gaming PC as a Plex Media server and would like to build a dedicated server to save cost on power bills.
Was looking into a Raspberry Pi 4 (8GB) version but my mate advised it is only good for local streaming. Would like to find something that can stream content while on the go.
Any information as to what device I should invest would be great. All my media is on a 10TB external HDD with USB3.0 compatibility.
Just in case it matters - your mate says the Pi is good for local streaming only. He will say that because normally one would use Plex to transcode to a suitable bit rate for managing your uplink when accessing your Plex server from outside your home network - and that's true enough. However, if you have (a) sufficient uplink in your internet connection, OR (b) your media is in a format that doesn't need transcoding (ie a low enough bit rate) - then the Pi can do the job.
Having said that, these days I prefer a Synology NAS (a Plus model for your task). It might seem too much money but there's a great deal you can do with these units. It might help with a great many other roles.